CONTENT 5.1 SEISMIC BEHAVIOUR ... - CIB-W18

33-16-3 B Källsner, J König
Thermal and mechanical properties of timber and some other materials
used in light timber frame construction
Summary
The Fire Part of Eurocode 5 gives the option of applying, simplified, more
complex and general design rules. For assessment of general design rules,
or the derivation of simplified design rules for thermal and mechanical
analysis, material properties are needed such as thermal conductivity, specific
heat capacity and reduced mechanical properties at elevated temperatures
in combination with effects of moisture. Unfortunately there is a
large variation of values given by different sources. This paper discusses
different values and the dependence of calibrated properties on the applied
model and gives the background of the values proposed to be adopted in
the Fire Part of Eurocode 5.
Conclusions
In the calibration procedure used, the main principle was to use thermal
properties that could be found in the literature and to modify them, where
necessary, in order to get results in agreement with results obtained from
testing of fire exposed timber or wall and floor assemblies. The thermal
properties should be calibrated such that they could be used independent
of the physical arrangement of the materials in the structures. Thermal
properties to be adopted in a design code cannot be true values as such;
they are rather apparent or fictitious values. They should reflect the physical
properties and phenomena in an understandable way such that designers
– who for this type of analysis should be specialists in the field of fire
design – can use them in an appropriate way. The thermal and design data
presented here give safe results and should therefore be suitable for adoption
in EN 1995-1-2.
34-16-1 I Totev, D Dakov
Influence of the strength determining factors on the fire resistance capability
of timber structural members
Introduction
The main objective of this research is to obtain data for the influences of
the strength determining factors on the fire resistance of softwood beams,
subjected to bending. The relationship between growth rate and charring
rate was researched. It is easy to establish the number of growth rings. It
allows rapid approximate assessment of the fire resistance through relationship
between growth rate and charring rate.
Knots and fissures are important factors for assessment of the behaviour
of the timber elements in fire conditions as well.
Conclusions
Relationships are obtained between the number of growth rings, charring
rates and the modulus of elasticity. Estimations for fire-resistance of exiting
timber structures are possible because it is easy to determine the number
of growth rings. The distance between the knots and bottom edge of
the beam is a useful bit of information about expected fire-resistance. Regrading
of the beams helps in carrying out the correct assessment. Methods
that predict fire resistance based on data about growth rate, disposition
and size of knots and fissures could be developed. They could be employed
by insurance companies when assessing the fire risk of existing
timber structures.
34-16-2 J König, B Källsner
Cross-section properties of fire exposed rectangular timber members
Summary
The Fire Part of Eurocode 5 gives the option of using methods of different
complexity for the determination of the uncharred residual cross section
and the reduction of strength and stiffness parameters. By using advanced
methods of heat transfer calculations, using the thermal properties of wood
and the char layer given in Draft prEN 1995-1-2, it is shown that the notional
charring rates given in the code are reasonable, allowing the designer
to disregard corner roundings. This paper gives the background of the
different methods for the reduction of strength and stiffness. Advanced
calculations using the thermo-mechanical properties of timber given in
Draft prEN 1995-1-2, show that the reduced cross section method gives
fairly accurate results for members in bending, while it is unsafe in relation
to the advanced method for members in compression or tension. The
reduced properties method, however, is unsafe for members in bending,
compression and tension.
CIB-W18 Timber Structures – A review of meeting 1-43 5 SPECIAL ACTIONS page 5.34